1. Technical Field
This disclosure relates to memory devices, and more particularly to a semiconductor memory device and a memory system including the same.
2. Discussion of the Related Art
The refresh operation of memory cells should be continuously performed even in a stand-by mode so as to retain data stored in the memory cell, e.g., that of a Dynamic Random Access Memory (DRAM) device. A self-refresh mode is widely used for DRAMs. The self-refresh mode is of the type adapted to perform the refresh operation of the memory cell with the lapse of a predetermined time after going into an operation stand-by mode, even though a separate control signal is not applied from an external source to the memory device. Once the self-refresh mode starts, it is preferable to perform the refresh operation of all memory cells in order to keep data. Thus, the memory devices employing the self-refresh mode have their own refresh regulation time (i.e. the minimum time required in performing the self-refresh mode).